Isomerization of xylenes



Dec- 15, 1953 D. A. M CAULAY ET AL ISOMERIZATION OF XYLENES Filed June 29. 1951 L I mm a m N n m mm hm mwHCwm N 7 mm 12.05,. 2 55: mm mm \w mm um L: m

Patented Dec. 15, 1953 Lien, Highland, Ind., assignors to Standard Oil Company,v Chicago, 11]., a. corporation of Indiana" Application 1m 29, 1951, Serial No. 234,414

15 Claims. (01. 260 -668) This invention relates to: the isomerizationv of para-xylene, ortho'xylene or a mixture of Ca aromatics. More particularly it. relates. to the production of meta-xylene by the isomerization of para-xylene and/or ortho-xylene. Still more particularly, it relates to the isomerization of para-xylene, ortho-xylene or mixtures of. Ca aromatics in the presenceoi a catalyst consisting. essentially of liquid hydrogen fluoride and BFs.

The present commercial polystyrene resins have a softening point below the boiling point of water. This defect has encouraged a search for resins of' this type with higher softening points. It has been foundthat substantially pure dimethylst'yrene polyme'rizes to a resin with a softening point in excess of 100 C. In the high temperature dehydrogenation of ethylxylenes to produce dimethylstyrenes, 1,3,5-ethylxyleno has been found to be a preferred feed stock. High purity meta-xylene is valuableas a starting ma terial for this synthesis. An-object of. our invention is the production of a high purity metaxylene fraction suitable for this use- Another object of our invention is to -effect xylene isomerization without encounteringside reactions such as cracking and. disproportionation of said xylenes. A further object is to avoid the severe operating conditions heretofore employed for eifectingxylene isomerization with HF BFa catalysts. Other objects will be apparcut as the detailed" descri'ptionof our invention proceeds.

Xylenes react with BFs (1 mol ofBFa per mol of xylene) to form complexes which are soluble in liquid HF. These complexes differ in stability; meta is the most stable and para the least stable. It i probable that the complex includes one or more mols of HF per mol of xylene-BFa-.

We have discovered that para-xylene-i'somerizes' to meta-xylene, and that ortho-xylene isomerize's.

to meta-xylene, when the xylene is complexed with sufficient BFs to render all the xylene soluble in liquid HF and the liquid HF solution of xylene-BF: complex is maintained at les than about 90 F. The degree of isomerization is dependent upon the length of time that the BF3- xylene complex liquid-HF solution ismaintained at the reaction temperature. The amount of meta-Xylene present in the product increases with increase in reaction time until a definite equilibrium composition is reached.

It is necessary that sufficient liquid HF be present to dissolve all the BFx-xylene complex formed. The presence of HF in excess of this minimum amount is preferable because the HF helps to catalyze the isomerization. Thus the amount of liquid HF used is between 50 volume percent, based on xylenes charged, to about 600 volume percent; preferably about to about 300 volume percent. should be used; we have found that particularly good: results are obtained.

when using about: 200 volume percent of liquid HF, based on xylene feed. Since Water reacts very rapidly with BFs to form undesired hydrates, the liquid HF should be substantially anhydrous and inv no case should more than 1 or 2% of water be present.

We have discovered that at about, ambient temperature the isomerization will proceed in appreciable. yield. only when all the xylenes are brought into solution in the liquid HF (which condition will be spoken of in. this specification as the homogeneous phase). The homogeneous phase can be attained with ortho-xylene when slightly less than 1 mol of BFa. is used per' mol' of ortho-x-yleneas the complex appears to solubilize the uncomplexed ortho-xylene. However, we prefer to use atleastl mol of. BF3 with orthoxylene asthe degree of isomerization increases with complete complexing of theiortho-xylene.

Because the stability of. the para-xylene BFs complex is less than that of the ortho-xyle'ne complex, at least 1 mol of BFs is needed per mol of para-xylene in order to attain ah'omogeneous phase. Although good results are obtained when using the minimum amount of BF; necessary to form a homogeneous phase, larger amounts can beused. We prefer to use from 1 to about 5 'mols of BE and particularly good results are obtained when using from about 1.5 to about 3 mols of BF: per molof xylene.

The presence of inert, HF-insoluble hydrocarbons such as propane, butane, pentane, lightretically, sufiicient BFz has been used tocomplex completely. all the xylenes present. The liquid HF contains an equilibrium mixture of the BF:- xyle'ne complex and free-xylene. As the diluent selectively draws out the free xylene, the complex dissociates to give more free-xylene. Thusif enough diluent is present, the ortho and paraxylene complexes can be more or less completely dissociated and the free-xylene removed by the diluent. The meta-xylene is so firmly held in the BFa-compl'ex that it is possible to selectively separate the para and ortho-xylenes from the These hydrocarbons are of the diluent that does not dissolve in the homogeneous phase (raflinate phase) are not isomerized even though a large excess of BFs may be present in the reactor. If the amount of dilumaximum possible conversion to the meta-isomer; product mixtures containing less than the maximum amount of the meta-isomer can be obtained by decreasing the reaction time. For

ent used is very large, isomerization of the para example, a product containing 50% para-xylene and ortho-xylenes may be substantially halted. and 50% meta-xylene can be obtained at 86 F. Therefore, in our process diluents should be in 11 minutes; at 68 F., 28 minutes; and at 0 F., avoided, at least in amounts large enough to 20 hours. form a separate phase distinct from the liquid Usually our process will be operated at ambient HF-BF; complex homogeneous phase. temperature. However, it is possible to operate We have found that the degree of isomerizaat temperatures as low as 0 F. and even lower if tion attainable in the homogeneous phase is the correspondingly increased reaction times to dependent upon both temperature and reaction attain the desired product composition can be time. The reaction temperature that may be tolerated. We prefer to operate at temperatures used is limited by the fact that at upwards of from about 50 to about 85 F. with about 75 F. about 90 F. appreciable amounts of undesirable representing a good compromise of temperature byproducts are obtained due to disproportionaand reaction time for a commercial process. t of t y1enes It does not appear to be As illustrations of the results obtainable by our possible to isomerize either the para-Xylene or p cess. d t from many ru s are presented in the ortho-xylene completely to the meta-isomer. 0 Tables I, II and III. At about 90 F. the equilibrium composition ap- The isomerization of para-xylene is illustrated pears to be about 95% meta-xylene and 5% paraby the runs in Table I. These data show very xylene for the para-isomerization; for the orthoclearly the effect of temperature and reaction isomerization at about 90 F., the equilibriu time on the composition of the product. Run 12 composition is about 90% meta-xylene and about shows t ffect of whemane as a q m; on the ortho-xylelle- The high meta-Xylene c011- degree of isomerization. Even though the extent of the equilibrium mixture is unexpected. tract phase Showed a conversion f 74% of the h thermodynamic equilibrium mixture xylenes contained therein to the meta-isomer, tams only abollt 60% m i i f it is noteworthy that 95% of the xylenes in the At about 90 the .l m raflinate phase were the para-isomer. Run 11 Xylene reaches f equlhbnum P shows that at a reaction temperature of 86 F. about 150 to 200 minutes. As the reaction tem and 1435 L m b t 2 perature is decreased the length of time needed mmubes Ion 0 a on to reach equilibrium increases so that at about of the total xylenes were disproportionated into 70 F. the reaction time must be from about 200 byproducts Such as benzene toluene and trito 350 minutes and about 60 F. the reaction time methylbenzenemust be fr about 3 to 609 minutes In Table II there are presented runs on the F th isomerization of ortho-xylene more isomerization of a mixture of meta-xylene, paratime is needed to reach equilibrium than is needed y e and ethylbenzene. In run 13 only 0.4 Of for the para-xylene isomerization, when both re- 40 a mol of BFa was used per mol of the feed. The actions are carried out at the same temperature. product distribution shows that the ethylbenzene y raising the ion temperature for the was disproportionated to 1,3-diethylbenzene, ortho-i somerization about 20 equilibrium can 1 3 5- 1 1 and other ethylxylenes Very 111 s the same tlme needed f the little isomerization of the para-xylene was obr z i n r p r -Xylene at the lower tained in this run even though a temperature of ggf mi a ZQ F Qg oft about 75 F. and 210 minutes reaction time were used. 1' m or O avm 1.spwpm 9 to Runs 14 and 15 are identical except for the undesirable by-pi oduets, applies to the 1somer1za amount of h qui d HF uaed These runs sho that tion of either the para-Xylene, the ortho-xylene, when the amo t mixtures of the two, or mixtures of isomeric 1 un o lqul HFwasmcreased 110m xylenes and ethylbenzene. At about 90 F. the 00 percnt P 200 Volume percent the ortho-xylene isomerization attains the equilibdegree of lsomenzatlon of the para-Xylene was mum composition in from about 200 to 300 increased by about 50%. Run 16 shows the effect utes, and at equilibrium is attained in 309 to on the degree of isomerization of complexing all 600 i t t about a the orthmisomer- 55 the xylenes. Taking into account the effect of ization attains equilibrium in from about 600 to the increased amounts of HF i un the de ree about 1000 minutes. of isomerization in run 16 is almost threefold The above reaction times apply to the case of greater than that of run 13.

TABLE I Isomerization of para-xylene RunNo -.llzle i 5 6'7'8'91011 12 Charge: I i

HF (V. percent on xylene) 200 200 200 200 200 200 200 200 200 200 200 BF; (mols/mol xylene) 1.01 1.58 1. 58 1.58 1.58 1.83 n-Heptane (V. perccntonrylene) 50 Temp.,1 37 37 a1 31 37 37 68 86 86 86 50 Reaction t1me,min 15 45 225 1,260 120 90 25 55 I 1, 435

Rail 1 Extr. Total Product distribution (mol. percent): I

m-Xylene 13 27 42 61 88 2s 68 so 89 95 95 5 74 61 p-Xylene s7 73 58 39 12 72 a2 20 11 5 5 95 2e 39 Percent dlsproportionation 0 0 0 0 0 0 0 0 0 0. 2 0 O 1 Contains 19% of feed'xylene. i Contains 8l% of feed xylene.

Run No 13 14 1s Charge: .m-Xylene, mols... 1.63 .1. 61 O. 81 0.82 p-Xylene, mols. 1. 62 1. 62 .81 .81 Ethylbenzene, mo .1. 62 1.62 .81 81 HF (V. percent on xylenes) .(100) '(100) '(200) {200) BFs (mols/mol xylenes') 0. 41 1.01 1.05 1.10 'n-Heptane (V. percent onxylenes). (100) Temp, F 75 70 70 75 Reaction time, min '210 30 30 30 Rad. 1 kt. "-lotal Percent Total Percent Total Percent Rafi. Ext. Total Percent Product distribution (mols): i I Benzene 0. 19 0. l0 0. 29 6. 0 0. 65 13. 4 0. 38 15. 6 0. l2 0. 10 0. 22 9. 2 60 1. 06 1.66 34. 1 2. 01 41. 5 1.19 49.0 06 1. 05 1. 11 '45. '4 1. 05 .37 1. 42 29. 2 .04 i 19.4 .30 12. 3 .37 .11 .48 :19. 7 .97 .26 1. 23 25. 2 .55 11.3 18 7. 4 .36 .07 43 17.6 .07 .07. 1. 4 17 3,5 .04 1. 6 .00 .02 .02 .8 .12 I 04 .16 3. 3 .53 10. 0 .83 13. 7 00 I .17 1'6 6.:5 .03 .01 .04 .8 .00 .01 .4 .00 .02 .02 .8

Percent p-xylene isomerized to m-xylene a; 12 42 63 41 TABLE III Isomerizatz'on of ortho-rylene Run No 17 '18 v 19 20 21 22 Charge: 1

HF (V. percent on'xylene) 200 200 200 200 200 200 BR; (mols/rnol xylene) 1.-60 1. 60 1. 60 1. 6O 1. 6O '1. 03 Temp, F 5t 56 56 56 56 68 Reaction time. 'min '25 100 230 400 1, 435 90 Product distribution: e

m-Xylene 7 43 57 82 44 o-Xylene v93 75 .57 43 18 56 Percent disproportionation 0 -0 0 v 0 0 '0 In Table III are presented data on the isomerization of ortho-xylene. Our data show that Within the error of the analytical pmcedu-res used, the isomerization of para-xylene in our process produces no ortho-xylene; and the isomerization of ortho-x-yl-ene in our process pr0- duces no para-Xylene. This is a wholly unexpected and very surprising result of our process.

The following typical runsil-lustrate the experimental procedure used and results obtainable by our process.

HUN 7 The apparatus employed was a 1570 m1. carbon steel autoclave fitted with .a 17.25 P. mechanical stirrer. A 258.5 gram (2.43 mole) sample of para xylene, 600 m1. of substantially anhydrous liquid HF and 170 grams (2.50 mols) of BFs were added to the reactor. The reaction mixture Was agitated at 68 for 9 0 minutes. At the end of this time the mixture was allowed to settle for 10 minutes.

The contents of the reactor were Withdrawn into a Dry Ice-cooled flask containing about 7 ml. of water. The flask containing the reactants and water was allowed to warm to room temperature. The decomposition of the El 's-complexes by the water resulted in the separation of an oil phase and an aqueous HF-BFa phase. The oil phase was Withdrawn and Washed with ammonium hydroxide to remove traces of dissolved HF and BFe. The oil product Was fractionated through a column containing 30 theoretical plates. In this run the distillation indicated that all the hydrocarbons consisted of C6 alkylbenzenes. The product distribution was determined by ultraviolet absorption analysis. This aha-ly sis indicated that only para-xylene and metaxylene were present in the hydrocarbon product.

The para-xylene had been isomerized to metaxylene to the extent of 68mo1. percent.

R-UN 12 Para-xylene, with volume percent n-heptane diluent, 200 volume percent of liquid HF and 1.83 mols of BF'3 per mol of para-xylene was introduced into the reactor. .After stirring for 1 20 minutes at 50 F., the reactor was found to contain two phases. The heavier extract phase was withdrawn into a flask containing water to decompose the BFs-COIIIDIGXBS. 'The raffinate phase was then withdrawn from the reactor and washed with ammonium hydroxide to remove traces of dissolved HF andBFa. The n-heptane was stripped from the raffinate phase leaving a hydrocarbon product representing 19% of the para-xylene 'feed; the raflinate xylenes analyzed 5% meta-xylene and 95% para-xylene. The distillation of thehydrocarbons .in the extract phase indicated only xylenes were present. Analysis of this product.

s'howed74% meta-xylene and 26% para-xylene. Thus even with a very large molar excess of BF3 present, that is, more than the theoretical 1 .mol per mol of xylene needed to complex all the xylene's, the addition of only 50% of diluent removed almost 20% of the para-xylene charged from the acid solution into the'diluent where essentially no isomerization took place.

RUN 6 levelsshows that the liquid HF has some catalytic effect on the degree of isomerization as well as acting as a solvent for the xylene-BFa complex.

Large scale operation The accompanying drawing shows one embodiment of our process for the production of substantially pure meta-xylene by the isomerization of para-xylene. It is to be understood that this embodiment is shown for purposes of illustration only and that many other variations of our process can be readily devised by those skilled in the art.

In this illustration the charge consists of paraxylene from a source ll. However, the charge could be a mixture of para and ortho-xylenes, ortho-xylene alone, a mixture of meta, paraxylene and ethylbenzene, or even the total xylene-ethylbenzene fraction such as is obtained from the hydroforming of petroleum naphthas. Liquid HF from source I2 is passed through valved line I3 into line H and on into line l5. BFs from source I6 is passed through a valved line i"! into line where it meets the liquid HF. Paraxylene from source I l passes into line l5 andvthe contents of line l5 are passed into mixer l8 where the para-xylene-BFa-liquid HF are thoroughly commingled. Mixer I8 is provided with a cooling coil [9- to withdraw the heat of reaction released during the formation of the BFz-xylene complex. through line 2| into reactor 22 which is provided with a coil 23. Coil 23 can be used either to cool or to heat the contents of the reactor in order to maintain relatively constant temperature in the reactor. Temperature in the reactor can be maintained at any point between about 0 F. and about 90 F.; preferably the maximum temperature is held below about 85 F. a temperature in the range of 65 to 75 F. gives shortest reaction times consistent with ease of temperature 1 control. The reactants are held in reactor for a time suflicient to obtain the desired degree of isomerization. This time may vary from as little as minutes at about 90 F. to more than 24 hours. We prefer to hold the reactor at about 75 F. for a reaction time of about 200 minutes.

The equilibrium composition of the product is almost entirely meta-xylene. If, however, an

essentially pure meta-xylene product is desired the para-xylene contaminant can be eliminated by introduction of a countersolvent in the form of a diluent. The reactants pass from reactor 22 into line 24 where they are contacted by the diluent (which serves also as a quench liquid) from source 26 which enters line 24 through valved line 21. The diluent must be inert to the action of liquid HF and/or BFs. Suitable materials are propane, butane, benzene, toluene, etc. The diluent is used in large enough quantity to dissolve substantially all the para-xylene into the diluent rich raffinate phase, which takes place even though enough BF; is present to theoretically complex all the xylenes. It is preferred that from about 200 to 400 volume percent, based on para-xylene feed, of diluent be used.

The diluted-reaction mixture passes through line 28, cooler 29, and line 3| into settler 32. The diluted reactants are cooled in order to decrease the isomerization of the meta-xylene that is present in the acid phase. The removal of the paraxylene by the diluent into the rafiinate phase normally would result in some isomerization of the meta-xylene to the equilibrium composition existing in the acid phase. Cooling of the re- The reactants pass from mixer 18 actants can be accomplished by the use of cold diluent alone or by the use of a heat exchanger. However, we prefer to use a combination of these methods.

In settler 32 the excess BF; is vented through line 33; the rafiinate phase is separated and passed through line 34 into stripper 35. Stripper 35 is provided with a reboiler 36 which provides the heat needed to separate the diluent from the para-xylene. The diluent vapors and the BF3 from settler 32 are taken overhead through line 31 through cooler-condenser 38 into separator 39.

In separater 39 the diluent is separated from liquid HF, saturated with 132%. The diluent can be recycled to line 21 for reuse in the process. The liquid HF-BFs solution passes out of settler 39 and is recycled to line I3 for reuse in the process. The free BF3 passes out of separator 33 and is recycled to line I! for reuse in the process. The para-xylene bottoms from stripper 35 are passed out of the stripper through line 4| and are recycled to source I I for reuse in the process.

The extract phase which contains liquid HF and substantially pure meta-xylene-BF; complex is withdrawn from settler 32 by line 45 and is passed into stripper 46. In order to prevent the isomerization of meta-xylene the decomposition of the complex is carried out under vacuum. While it is not absolutely necessary to do so, the operation may be facilitated by the use of a stripping agent such as propane or butane. The stripping agent herein, butane, is added to stripper 46 from source 41. The stripping agent, HF and BFa pass out of stripper 46 through line 48, through vacuum pump 49 and through cooler 5| into settler 52. Cooler 5| condenses the butane and the HF. Free BF; is removed from settler 52 through line 53; this is recycled to line [1 by way of valved line 54. The butane stripping agent is removed from settler 52 through line 55 and is recycled to stripper 46. The liquid HF, saturated with BF3, is removed from settler 52 through line 51 and recycled, for reuse in the process, to line [4 by way of line 58. The substantially pure meta-xylene is removed from stripper 45 through line 6|.

When the feed xylene to our process consists of ortho-xylene it is not necessary to take as stringent precautions to prevent the isomerization of the meta-xylene to the ortho form. In this case the use of a diluent to extract the ortho-xylene from the acid phase may be dispensed with if desired. The reaction mixture may be cooled and sent to the stripper where the HF and BF3 are removed under vacuum. The total product is sent to a fractionating tower where a substantially pure ortho-xylene fraction and a substantially pure meta fraction are easily produced due to the difference in the boiling point of these two isomers.

We have previously discovered that ethylbenzene does not complex with HF and BF: but is very rapidly and substantially completely disproportionated in the presence of liquid HF and BF: to benzene, 1,3-diethylben2ene and unreacted ethylbenzene as described in our Patent U. S. 2,528,893. The benzene and unreacted ethylbenzene are very readily removed from the homogeneous phase by inert, HF-insoluble diluents such as propane and butane. The disproportionation of ethylbenzene can be carried out simultaneously with the isomerization of the para and ortho-xylenes, if sufficient BF; is added to complex the diethylbenzene and ethylxylenes formed in addition to the amount needed to complex the xylen s present. Although, only 0.5 mol of BFs are needed theoretically, we prefer to use about 1. mol oi BFs per mol oiethylbenzene, in order to maximize the degree of d proportionation.

Our process can operate, on a feed consisting of a mixture of CB. aromatics by using about 1 mol of 131% per mol of ethylbenzene present in the C8 aromatic and atleast 1 mol OfBFs per mol of xylenes present. When operating on. such a feed the reaction time should be long, enough to disproportionate substant ally all the, ethylbenzene as well as long enough to attain the degree. of isomerization desired. We prefer to extract the mixture leaving. the reactor with bu; tane to remove the benzene, unreacted para (and ortho) Xylene and unreactedethylbenzene from. the acid phase. Thus we. remove the HF and BFa from the mixture of metaxylene and diethylbenzene by vacuum strippingand there.

after separate the substantially pure metaxylene from the diethylbenzene and ethylxyl'enes by distillation.

We claim: 7

1. A process, for the isomerization of paraxylene to a product containing in excess of about 85 mol percent of meta-xylene which process comprises contacting under substantially anhydrous conditions said para-xylene with from at least 1 to-v about 3 mols of BFs per mol of para.- xylene and with from about 100 to 300 .volume percent, based .on said para-xyleneof liquid HR in a. single; phase homogeneous solution at; a tern. perature between about 60 F. and 90 F. for a time from about 150 to about 600 minutes, wherein the longer times are associated with the lower temperatures, and separating the HF and BF: from a product consisting of at least about 85 mol percent of meta-xylene and the remainder essentially para-xylene.

2. A process for the isomerization of paraxylene to a product containing in excess of about 85 mol percent of meta-xylene which process comprises contacting under substantially anhydrous conditions said para-xylene with from at least 1 to about 3 mols of BF3 per mol of paraxylene and with from about 100 to 300 volume percent, based on para-xylene, of liquid HF in a single phase homogeneous solution and separating the HF and BFs from a product consisting of at least about 85 mol percent of metaxylene and the remainder essentially paraxylene and wherein the contacting is carried out at a temperature-time relationship substantially as follows:

Minutes 3. A process for the isomerization of orthoxylene to a product containing in excess of about 80 mol percent of meta-xylene, which process comprises contacting under substantially anhydrous conditions said ortho-xylene with from at least 1 mol to about 3 mols of .BFs per mol of ortho-xylene and with from about 100 to 300 volume percent, based on ortho-xylene, of liquid HF in a single phase homogeneous solution at a temperature between about 70 F. and 90 F. for a time from about 200 to about 1000 minutes, wherein the longer times are associated with the 1'0 lower temperatures; and separatin the: HF and BFa from a product consisting of at least about. mol percent oilmeta-xy-lene and the remainder essentially ortho-xylene 4. A process. vfor the isomerization of orthorxylene tov a product containing inexeess. of about 80. mol percent of. meta-xylene, which; process comprises. contacting under substantially anhydrous conditions said ortho-xylene. with from at leastv 1 to about 3 mols of, BFs per mol, of ortho-xylene and with from about 100- to 300 volume percent, based on ortho-xylene, of liquid HE in a singlephase homogeneous solution and separating the HF and 3E3 from a product consisting of at least about 8.0 mol percent of metaxylene and the remainder essentially ortho- Xylene, and wherein. the contactingis carried out at a temperature-time relationship substantially as follows:

5. A process which comprises contactingun is present in an amount. appreciably less than the theoretical thermodynamic. equilibrium amountwith at least a ut 1 ml. of B ss D6 mol of xylene in said feed and with at least sufficient liquid HF to form a single phase homogeneous solution of said feed and BFs in said liquid HF, maintaining said solution at a temperature between about 0 and 90 F. for a time at least sufiicient to produce a reaction product mixture containing an amount of meta-xylene appreciably greater than the theoretical thermodynamic equilibrium amount, and removing the HF and BF: from the reaction product mixture.

6. The process of claim 5 wherein said liquid HF is present in an amount between about 50 and 600 volumepercent based on said feed.

7. The process of claim 5 wherein the temperature is maintained between about 50 and F.

8. The process of claim 5 wherein said feed consists essentially of para-xylene.

9. The process of claim 5 wherein said feed consists essentially of ortho-xylene.

10. The process of claim 5 wherein said product mixture contains at least about 80 mol percent of meta-xylene.

11. The process of claim 5 wherein (a) the single phase homogeneous solution of HF, reaction product mixture and BFs is contacted at a temperature between about 0 and F. with a liquid hydrocarbon diluent that is substantially insoluble in and inert to the action of liquid HF-BF: agent and that is readily separable from xylene by a distillation process, in an amount between about and 300 volume percent based on said feed, b) a railinate phase, which consists essentially of said diluent and dissolved xylenes, is separated from an extract phase consisting essentially of HF, BR? and xylenes, and (c) said extract phase is processed to recover a xylene product that is substantially pure meta-xylene.

12. A process which comprises contacting under substantially anhydrous conditions a feed comprising essentially a member of the glass c m.

sisting of (a) a natural mixture of Ca aromatic.

hydrocarbons and (b) a mixture of C8 aromatic hydrocarbons derived by distillative separation of a natural mixture of Ca aromatic hydrocarbons, which feed contains an amount of meta-xylene appreciably less than the theoretical thermodynamic equilibrium amount, with at least about 1 mol of BFa per mol of Ca aromatic hydrocarbons in said feed and with at least suflicient liquid HF to form a single phase homogeneous solution of said feed and associated BFs in said liquid HF, maintaining said solution at a temperature between about and 90 F. for a time at least sufficient to produce a reaction product mixture containing meta-xylene appreciably in excess of the theoretical thermodynamic equilibrium amount, removing the HF and BF: from the reaction product mixture, and recovering a product mixture of Ca aromatic hydrocarbons containing an amount of meta-xylene appreciably in excess of the theoretical thermodynamic equilibrium amount from said reaction product mixture.

13. The process of claim 12 wherein (i) the solution of HF, reaction product mixture and BF: is contacted at a temperature between about 0 and 90 F. with a liquid hydrocarbon diluent that is substantially insoluble in and inert to the action of liquid I-IF-BFa agent and that is readily separable from xylene by a distillation process, in an amount between about 100 and 300 volume percent based on said feed, (ii) a raflinate phase, which consists essentially of said diluent, product benzene, ethylbenzene and xylenes, is separated from an extract phase consisting of HF, BF3 and aromatic hydrocarbons and (iii) said extract phase is processed to recover a Ca-aromatic hy- 12 drocarbon product that is substantially pure meta-xylene.

14. The process of claim 12 wherein the Ca aromatic hydrocarbon product mixture contains at least about 80 mol percent of meta-xylene.

15. A process which comprises contacting under substantially anhydrous conditions a feed comprising essentially a member of the class consisting of ortho-xylene, para-xylene, mixtures thereof and mixtures of meta-xylene and at least one other xylene isomer wherein the meta-xylene is present in an amount appreciably less than the theoretical thermodynamic equilibrium amount, with between about 1 mol and 3 mols of BF: per mol of xylene in said feed and with between about 100 and 300 volume percent of liquid HF based on said feed to form a single phase homogeneous solution of said feed and BF3 in said liquid HF, maintaining said solution at a temperature between about and 85 F. for a time at least sufficient to produce a reaction product mixture containing at least about mol percent of metaxylene but not long enough to produce essentially any side-reaction products and removing the HF and BE; from the reaction product mixture.

DAVID A. McCAULAY. ARTHUR P. LIEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,521,444 Brooke et al Sept. 7, 1950 2,527,825 Kemp Oct. 31, 1950 2,564,073 Lien et al Aug. 14, 1951 

15. A PROCESS WHICH COMPRISES CONTACTING UNDER SUBSTANTIALLY ANHYDROUS CONDITION A FEED COMPRISING ESSENTIALLY A MEMBER OF THE CLASS CONSISTING OF ORTHO-XYLENE, PARA-XYLENE, MIXTURES THEREOF AND MIXTURES OF META-XYLENE AND AT LEAST ONE OTHER XYLENE ISOMER WHEREIN THE META-XYLENE IS PRESENT IN AN AMOUNT APPRECIABLE LESS THAN THE THEORETICAL THERMODYNAMIC EQUILIBRIUM AMOUNT, WITH BETWEEN ABOUT 1 MOL AND 3 MOLS OF BF3 PER MOL OF XYLENE IN SAID FEED AND WITH BETWEEN ABOUT 100 AND 300 VOLUME PERCENT OF LIQUID HF BASED ON SAID FEED TO FORM A SINGLE PHASE HOMOGENEOUS SOLUTION OF SAID FEED AND BF3 IN SAID LIQUID HF, MAINTAINING SAID SOLUTION AT A TEMPERATURE BETWEEN ABOUT 50* AND 85* F. FOR A TIME AT LEAST SUFFICIENT TO PRODUCE A REACTION PRODUCT MIXTURE CONTAINING AT LEAST ABOUT 80 MOL PERCENT OF METAXYLENE BUT NOT LONG ENOUGH TO PRODUCE ESSENTIALLY ANY SIDE-REACTION PRODUCTS AND REMOVING THE HF AND BF3 FROM THE REACTION PRODUCT MIXTURE. 